Photoanodes Consisting of Mesoporous Anatase TiO₂ Beads with Various Sizes for High-Efficiency Flexible Dye-Sensitized Solar Cells

The synthesis and characterization of TiO 2 beads and the use of them in the photoanodes of all-plastic flexible dye-sensitized solar cells (FDSCs) are reported. Pure anatase TiO 2 beads having different sizes and characteristics were first made using a novel two-step chemical method under different conditions. Photoanodes consisting of the beads as scattering layers were then fabricated. The use of beads largely enhances the dye loading and gives highly effective light scattering, leading to improved light absorbance. The resulting cells were evaluated for the electron diffusion time, electron lifetime, charge collection efficiency, incident photon-to-electron conversion efficiency, electron injection efficiency, and IV characteristics. The pure anatase TiO 2 beads, having low oxygen vacancy concentrations and directional attached grains, lead to more photoelectrons and enhance the electron diffusion, giving very short diffusion times. We have demonstrated for the first time that the use of beads, having diameters ranging from 250 to 750 nm, enhances the light-to-electricity conversion efficiency of FDSCs having plastic substrates by as much as 28%. The cell conversion efficiency is also enhanced from 4.3 to 5.5%.